In the related art, transistors having breakdown voltages different from each other are used in an integrated circuit in some cases. For example, when a signal having a relatively high voltage level is output towards a transistor having a relatively low breakdown voltage, it is necessary to shift (lower) the voltage level of the signal by using a transistor having a relatively high breakdown voltage.
To perform the level shift, a step-down circuit can be employed. That is, transistors used in the step-down circuit may need to have a breakdown voltage higher than input voltages supplied thereto.
The breakdown voltage of a transistor may be adjusted by varying the gate film thickness of the transistor. However, this complicates the manufacturing process because manufacturing transistors with varying gate thicknesses is more difficult than manufacturing transistors with the same gate thickness.